I recognized the voices as those of Ker Karraje and Engineer Serko. The two men stopped close to where I was lying, and continued their conversation in English--which is the language generally used in Back Cup. I was therefore able to understand all that they said.
They were talking about Thomas Roch, or rather his fulgurator.
"In a week's time," said Ker Karraje, "I shall put to sea in the _Ebba_, and fetch the sections of the engines that are being cast in that Virginian foundry."
"And when they are here," observed Engineer Serko, "I will piece them together and fix up the frames for firing them. But beforehand, there is a job to be done which it seems to me is indispensable."
"To cut a tunnel through the wall of the cavern."
"Oh! nothing but a narrow passage through which only one man at a time could squeeze, a hole easy enough to block, and the outside end of which would be hidden among the rocks."
"I have often thought about the utility of having some other way of getting out besides the submarine tunnel. We never know what the future may have in store for us."
"But the walls are so thick and hard," objected Ker Karraje.
"Oh, with a few grains of Roch's explosive I undertake to reduce the rock to such fine powder that we shall be able to blow it away with our breath," Serko replied.
It can easily be imagined with what interest and eagerness I listened to this. Here was a ray of hope. It. was proposed to open up communication with the outside by a tunnel in the wall, and this held out the possibility of escape.
As this thought flashed through my mind, Ker Karraje said:
"Very well, Serko, and if it becomes necessary some day to defend Back Cup and prevent any ship from approaching it----. It is true," he went on, without finishing the reflection, "our retreat would have to have been discovered by accident--or by denunciation."
"We have nothing to fear either from accident or denunciation," affirmed Serko.
"By one of our band, no, of course not, but by Simon Hart, perhaps."
"Hart!" exclaimed Serko. "He would have to escape first and no one can escape from Back Cup. I am, by the bye, interested in this Hart. He is a colleague, after all, and I have always suspected that he knows more about Roch's invention than he pretends. I will get round him so that we shall soon be discussing physics, mechanics, and matters ballistic like a couple of friends."